Experiments will be performed on in vitro rabbit retina maintained under different states of physiological activity by changing the illumination (i.e., darkness, steady light, flashing light) or by blocking neurotransmission by increasing the Mg ions/Ca ions ratio in the medium. Energy metabolism will be monitored using the decrease in medium O2 as a measure of oxidative metabolism and the increase in medium lactate as a measure of glycolysis. Some experiments are designed to examine the association between type of energy metabolism (oxidative or glycolytic) and the type of physiological activity (dark current of photoreceptors or transmissson through inner retina). The energy cost of dark current and of transmission through inner retina will be estimated. The role of carbonic anhydrase in pH maintenance, and the use of lactate as substrate, will be examined in retinas maintained under physiological conditions. Uptake of 2-deoxyglucose (2DG) will be correlated with levels of energy metabolism and physiological activity, and radioautographs with 3H-2DG will be used to locate sites of uptake. Changes in glycogen will be measured to assess its role in the normal economy of retina. Response (if any) to varying pO2 through the physiological range will be examined and an attempt made to demonstrate O2 toxicity in vitro.